The present invention relates to Stirling cycle hot gas engines and particularly to Stirling cycle engines capable of operating reversibly.
Previously known Stirling cycle engines of the type including a displacer to move the working fluid through a heat exchanger unit, such as those disclosed in Johnson U.S. Pat. No. 3,460,344 and Knoos U.S. Pat. No. 3,698,182, have utilized fixed relationships between the motion of the displacer and the motion of the power piston. The amount of power output has been controlled by the variation of the amount of heat supplied to the working fluid, and by the variation of the amount of dead space, the volume within the system which is not swept by the movement of the pistons and displacers.
Knoos discusses the use of plenums to vary the amount of dead space, while Johnson disclosed a chamber having a variable volume used to accomplish the same purpose. While the engines disclosed by Knoos and Johnson can thus respond quickly to changes in load or desired changes of speed, the engines are unidirectional and reversal of the direction of rotation of an output shaft must therefore be accomplished by means external of the engine, such as by changing gear relationships.
Another problem inherent in engines of this type is that the high pressure at which the working fluid is commonly maintained causes a great deal of difficulty in sealing openings in the engine casing through which shafts extend, to prevent loss of the working fluid into the surrounding atmosphere. The working fluid is commonly a nonatmospheric gas having desired thermodynamic properties and must be retained to maintain efficiency of the machine.
What is needed, therefore, is an improved system for controlling the operation of a Stirling cycle engine to provide reversability and improved responsiveness to changes in the desired power output of the engine, and an improved type of seal for use where a shaft, particularly an oscillating shaft, extends through the casing wall of such an engine.